The biotech industry has recently made great progress in producing a large number of recombinant human peptides and proteins that possess therapeutic potential. Several of the recombinant proteins such as growth hormones and humanized monoclonal antibodies have already been used clinically to treat human diseases [2]. It is estimated that the protein therapeutic market will grow rapidly at a compound annual growth rate of 10.5%, and will double in market value from 2003 to 2010 [3]. This expansion of protein therapeutics raises many issues in the pharmaceutical industry regarding the formulation and dosage design due to the difference between proteins and small molecular drugs. The most urgent issue to unlock the potential of these new drugs is to develop an oral dosage form for protein drugs, since this route of administration is the most convenient and economical. However, due to the biophysical makeup of protein-based drugs, namely, their large and bulky size, charge and hydrophilicity, and sensitivity to digestive enzymes, achieving oral delivery of these therapeutic agents into the tissues of choice or across epithelial barriers of choice remains difficult [4].
Because most of the protein and peptide drugs today are used for the treatment of chronic diseases, such as insulin for diabetes, frequent injections can cause inconvenience, poor compliance, and adverse side-effects to the patients. Therefore, non-invasive delivery systems for proteins and peptides, especially those utilizing the most convenient oral, route of administration, has long been sought by the pharmaceutical industry.
Despite the great efforts that have been directed towards this area of research, there is no established method for the oral delivery of these drugs. Therefore, there is an urgent need for a novel approach to the design of fusion proteins that can serve as drug delivery systems for delivering pharmaceutically relevant proteins via oral administration.